Lithos 46 Ž1999. 367–392
Emplacement, petrological and magnetic susceptibility
characteristics of diverse magmatic epidote-bearing granitoid
rocks in Brazil, Argentina and Chile
A.N. Sial
a,)
, A.J. Toselli
b,1
, J. Saavedra
c,2
, M.A. Parada d , V.P. Ferreira
a
a
NEG-LABISE, Department of Geology, Federal UniÕersity of Pernambuco, Recife, P.O. Box 7852, 50732-970, Brazil
Instituto Superior de Correlacion Geologica,
UniÕersidad Nacional de Tucuman, Miguel Lillo, 205, San Miguel de Tucuman 4000,
´
Argentina
Consejo Superior de InÕestigaciones Cientıficas,
Instituto de Recursos Naturales y Agrobiologia, Apartado 257, Salamanca 37080, Spain
´
d
Department of Geology, UniÕersity of Chile, Casilla 13518, Correo 21, Santiago, Chile
b
c
Received 1 December 1997; accepted 16 July 1998
Abstract
Magmatic epidote ŽmEp.-bearing granitoids from five Neoproterozoic tectonostratigraphic terranes in Northeastern ŽNE.
Brazil, Early Palaeozoic calc-alkalic granitoids in Northwestern ŽNW. Argentina and from three batholiths in Chile have
been studied. The elongated shape of some of these plutons suggests that magmas filled fractures and that dyking was
probably the major mechanism of emplacement. Textures reveal that, in many cases, epidote underwent partial dissolution
by host magma and, in these cases, may have survived dissolution by relatively rapid upward transport by the host magma.
In plutons where such a mechanism is not evident, unevenly distributed epidote at outcrop scale is armoured by biotite or
near-solidus K-feldspar aggregates, which probably grew much faster than epidote dissolution, preventing complete
resorption of epidote by the melt. Al-in-hornblende barometry indicates that, in most cases, amphibole crystallized at P G 5
kbar. Kyanite-bearing thermal aureoles surrounding plutons that intruded low-grade metamorphic rocks in NE Brazil support
pluton emplacement at intermediate to high pressure. mEp show overall chemical variation from 20 to 30 mol% Žmole
percent. pistacite ŽPs. and can be grouped into two compositional ranges: Ps 20 – 24 and Ps 27 – 30 . The highest Ps contents are
in epidotes of plutons in which hornblende solidified under P - 5 kbar. The percentage of corrosion of individual epidote
crystals included in plagioclase in high-K calc-alkalic granitoids in NE Brazil, emplaced at 5–7 kbar pressure, yielded
estimates of magma transport rate from 70 to 350 m yeary1. Most of these plutons lack Fe–Ti oxide minerals and Feq3 is
mostly associated with the epidote structure. Consequently, magnetic susceptibility ŽMS. in the Neoproterozoic granitoids in
NE Brazil, as well as Early Palaeozoic plutons in Argentina and Late Palaeozoic plutons in Chile, is usually low
Ž- 0.50 = 10y3 SI., which is typical behavior of plutons which crystallized under low f O 2 Žilmenite-series granitoids.,
although FerŽFe q Mg. ratios in hornblende Ž0.40–0.65. indicate crystallization under high f O 2 . Mesozoic to Tertiary
calc-alkalic plutons in Chile, however, exhibit iron oxide minerals and MS values ) 3.0 = 10y3 SI, typical of magnetite-
)
1
2
Corresponding author. E-mail: [email protected]; [email protected]
E-mail: [email protected].
E-mail: [email protected].
0024-4937r99r$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
PII: S 0 0 2 4 - 4 9 3 7 Ž 9 8 . 0 0 0 7 4 - 7
368
A.N. Sial et al.r Lithos 46 (1999) 367–392
series granitoids crystallized under higher oxygen fugacity. In NE Brazil, Argentina and Chile, it seems that mEp is more
common in Precambrian to Palaeozoic ilmenite-series granitoids, while its occurrence in magnetite-series granitoids is more
restricted to Mesozoic to Tertiary granitoids. q 1999 Elsevier Science B.V. All rights reserved.
Keywords: Magmatic epidote; Barometry; Magnetic susceptibility; Magma transport rate; Oxygen fugacity
1. Introduction
Although it has been known since the last century
that epidote occurs as a magmatic phase in granitic
rocks ŽKeyes, 1893., it was only after experiments
by Naney Ž1983., which demonstrated that epidote
could be stable above the solidus in granite and
granodiorite, that its occurrence became a matter of
petrologic interest ŽZen and Hammarstrom, 1984.. It
was accepted by that time that the occurrence of
magmatic epidote ŽmEp. in granitic rocks, at moderate to high pressure Ž6–8 kbar., was partly a function
of magma composition and partly of depth of emplacement. Other factors controlling naturally occurring mEp, however, are still debated, since plutons
of apparently similar chemical composition, crystallized at similar pressure, may or may not carry mEp.
The combination of recent experiments on epidote
dissolution kinetics ŽBrandon et al., 1996. and on its
stability in granitic melts ŽSchmidt and Thompson,
1996. suggests that epidote can be a powerful tool
for estimating intrusion conditions such as crystallization depth, oxygen fugacity and upward transport
rate of melt.
Brandon et al. Ž1996. reacted epidote with natural
granodioritic glass at pressures above and below the
stability limit of mEp. At high pressure experiments
Ž1150 Mpa, 7808C. there was no evidence of reaction between epidote and the granitic melt, whereas
low pressure experiments Ž450 MPa, 7508C. resulted
in epidote with irregular rims due to dissolution.
These authors modelled epidote dissolution in granitic
magmas as a relatively fast process and concluded
that the presence of mEp in calc-alkalic granitoids
implies fast upward transport probably via dyking
rather than diapirism.
Schmidt and Thompson Ž1996. studied the stability of epidote in calc-alkalic magmas and demon-
strated that, at water-saturated conditions and f O 2
buffered by NNO, epidote has a wide magmatic
stability field in tonalite, with a minimum pressure of
about 5 kbar. Experiments performed with f O 2
buffered by HM show that the stability field of
epidote is enlarged down to 3 kbar pressure.
In this study, mEp-bearing granitoid plutons from
northeast Brazil, Northwestern ŽNW. Argentina and
Chile were selected with the aim of identifying those
features which mEp in diverse mEp-bearing granitoids have in common and how these features help to
understand intrusion conditions.
2. Geological setting and petrography
Distinguishing magmatic from secondary epidote
in granitoids is not always straightforward. To
achieve this, the textural criteria described by Zen
and Hammarstrom Ž1984. including, among others,
chemical zonation of epidote, the presence of allanite-rich core, embayed contacts with plagioclase and
quartz, wormy Žalmost myrmekitic. contacts, as well
as chemical criteria ŽTulloch, 1979. based on the
pistacite ŽPs. content of epidote ŽPs s molar
wFe 3qrŽFe 3qq Al.x = 100., have been adopted in
the present study. mEp typically has - 0.2% TiO 2
by weight, whereas secondary epidote replacing biotite has ) 0.6% TiO 2 ŽEvans and Vance, 1987.. In
all of the plutons in the present study, modal abundances of mEp are low ŽF 5 vol.%..
2.1. Northeastern (NE) Brazil
mEp-bearing granitoids of Neoproterozoic age are
widespread in NE Brazil. They have been identified
A.N. Sial et al.r Lithos 46 (1999) 367–392
within five Neoproterozoic tectonostratigraphic terranes wSerido´ ŽST., Cachoeirinha–Salgueiro ŽCST.,
Riacho do Pontal ŽRPT., Alto Pajeu´ ŽAPT. and the
369
Macurure´ ŽMT.x; and belong to calc-alkalic, high-K
calc-alkalic, shoshonitic and trondhjemitic series
ŽFerreira et al., 1997; Fig. 1.. Whole-rock chemical
Fig. 1. Simplified geological map of Northeast Brazil, indicating locations of Neoproterozoic mEp-bearing granitoids, distributed in five
tectonostratigraphic terranes ŽI: Serido,
´ II: Cachoeirinha–Salgueiro, III: Riacho do Pontal, IV: Alto Pajeu,
´ and V: Macurure´ terranes..
370
A.N. Sial et al.r Lithos 46 (1999) 367–392
data for these plutons are presented and discussed in
Sial Ž1986, 1990. and Sial and Ferreira Ž1988..
mEp exhibits four textural relationships in these
rocks: Ž1. embayed or in vermicular contact with
unaltered plagioclase; Ž2. rimmed by biotite, with
zoned allanite core, Ž3. enclosing patches of hornblende, and Ž4. partially enclosed by biotite, in the
interstices of K-feldspar aggregates. All of these
textural types are found in each of the above-mentioned series of granitoids, with the exception of the
type 4 which is restricted to the high-K calc-alkalic
group.
Calc-alkalic mEp-bearing granitoids are found in
the ST, CST, RPT and MT. In the latter two, granitoids exhibit similar textural relationships and geochemical characteristics.
Plutons in the CST intrude low-grade meta
Žmarine. turbidites ŽFig. 1., and are typically round
to elongate in shape, containing calcic amphibole
and biotite as the main mafic phases. mEp occurs as
large crystals, up to 2 mm long, and is substantially
less abundant when clinopyroxene Ždiopside–salite.
is present. This is consistent with experiments by
Schmidt and Thompson Ž1996, p. 470., on watersaturated tonalitic melts, which demonstrate that
‘‘melting of epidote above the clinopyroxene-in reaction is directly related to the appearance of
clinopyroxene, that is, with increasing temperature
modal increase in clinopyroxene is directly proportional to modal epidote decrease’’ Žepidote q
hornblendeq H 2 O s clinopyroxeneq liquid..
Around two of these plutons, kyanite-bearing
black-spotted thermal aureoles are developed and
characterized by fine-grained mica foliation ŽCaby
and Sial, 1996.. According to the petrogenetic grid
of Xu et al. Ž1994., the assemblage garnet, kyanite,
staurolite, muscovite with Si - 3.1, biotite, plagioclase and quartz observed in these aureoles suggest T
around 6708C and P s 7.5 " 0.5 kbar ŽFig. 2.. Quartz
and rutile inclusions in garnet attest to peak P ( 9
kbar during garnet growth ŽBohlen et al., 1983..
Two types of amphibole-rich clots are observed in
the mEp-bearing granitoids in the CST. The first
type consists of deep-green calcic amphibole aggregates Žfractionated from the host magma. and the
second one, which exhibits a fabric, is fine-grained,
angular, and up to 15 cm long. This second type is
composed of actinolitic amphibole, with margins of
Mg-hornblende, and regarded as fragments from the
source picked up by the granodioritertonalite magmas ŽSial et al., 1995.. Often, the second type is
armoured by a layer of biotite and amphibole which
prevented further interaction with the host magma.
mEp-bearing calc-alkalic plutons in the ST ŽFig.
1. intruded intermediate to high-grade metasedimentary rocks. These occur as tonalitic dykes and sheets
Žmodal epidote up to 5% per volume. and as elongated granodioritic plutons. In the Rio Piranhas basement, to the west of the ST, calc-alkalic to high-K
calc-alkalic plutons Ž1, 6 and 7, Fig. 1. also contain
mEp.
In the MT ŽFig. 1., calc-alkalic granodiorites to
tonalites intruded intermediate-grade metasediments
locally generating thermal aureoles with stauroliteq
cordieriteq garnet porphyroblasts ŽMcReath et al.,
1993.. The calc-alkalic plutons of the MT, late to
post-kinematic according to Davison and Santos
Ž1989., are similar in textures, mineralogy and geochemical characteristics to those of the CST. The
metaluminous Gloria Norte and Coronel Joao
˜ Sa´
plutons are among the better known and these contain amphibole-rich clots which are similar in size,
mineralogy and textures to those described in the
CST mEp-bearing plutons.
High-K calc-alkalic metaluminous mEp-bearing
granitoids are mainly found in the APT ŽBrejinho,
Tavares, Caldeirao
˜ Encantado, Conceiçao
˜ das Creoulas and Riacho do Ico´ plutons; Fig. 1.; and one of
these plutons is found in the ST ŽSao
˜ Rafael.. They
intrude gneisses to migmatites in the APT and micaschists and gneisses in the ST. These granites
consist of coarse-grained porphyritic ŽK-feldspar
megacrysts in places up to 10 cm long. granodiorite
and granite with subordinate quartz monzodiorite to
quartz monzonite. mEp accounts for up to 1.5% per
volume. Locally, quartz diorite synplutonic dykes are
observed in outcrops where co-mingling and partial
mixing of granodiorite and quartz diorite magmas
took place.
mEp was observed in only one shoshonitic monzogranite in NE Brazil, at the eastern portion of the
Teixeira batholith ŽFig. 1. next to the northern margin of the APT. Among the mafic minerals, ferroedenite is the main phase which, in places, forms
agglomerates. Primary epidote is found as euhedral
to subhedral crystals included in biotite or, less
A.N. Sial et al.r Lithos 46 (1999) 367–392
371
Fig. 2. P–T plot for mineral assemblages in high-pressure, kyanite-bearing thermal aureoles observed around mEp-bearing granodiorites
Že.g., Angico Torto and Santo Antonio Creek plutons. in the Cachoeirinha–Salgueiro terrane, NE Brazil ŽCaby and Sial, in preparation..
often, at the borders of amphibole, in a textural
relationship similar to that described by Zen and
Hammarstrom Ž1984.. Some epidote grains have allanite cores.
mEp is also observed in two leucocratic trondhjemitic tonalite to granodiorite plutons: the Palmeira
pluton, which intruded gneisses of the APT, and the
Serrita pluton that intruded medium-grained
metapelites of the Salgueiro Group in the CST ŽFig.
1.. These plutons exhibit magmatic foliations, and
are almost totally devoid of enclaves. Mafic minerals
occupy less than 10% per volume and epidote is
present in low abundance Ž- 1%. as both primary
and secondary phases.
2.2. NW Argentina
In NW Argentina, mEp-bearing granitoids are
mainly identified in two regions ŽToselli et al., 1997;
Fig. 3. namely in the Pampean Ranges that correspond to a series of large N–S trending, tilted fault
blocks, composed of Early Palaeozoic granitoids,
and in the Famatina geological province ŽFGP., located between the Western and Eastern Pampean
Ranges, composed of Neoproterozoic to Early Cam-
372
A.N. Sial et al.r Lithos 46 (1999) 367–392
Fig. 3. Simplified geological map of northwest Argentina, indicating locations of occurrence of Early Paleozoic magmatic epidote-bearing
˜ ˜
granitoids along the Tafi Megafracture Ž1: Loma Pelada, El Infiernillo, Nunorco
Grande, La Angostura, El indio, and 2: Cafayate. and in the
FGP Ž5: Paiman–Copacabana, Cerro Toro, Nunorco,
Sanogasta,
Cerro Blanco, Paganzo; 6: San Agustin and 7: Serra de los Llanos
˜
˜
batholiths.. These two granitic belts are separated by a set of Early Paleozoic cordierite-bearing granitoids.
brian metamorphic rocks overlain by younger marine
sedimentary rocks.
In the Pampean Ranges, the NNW-trending Tafi
Megafracture ŽBaldis et al., 1975., active since Early
Fig. 4. Geological maps of the three areas of occurrence of calc-alkalic mEp-bearing granitoids in Chile: Ža. High Andes Cordillera, Žb.
Southern Coastal batholith and Žc. North Patagonian batholith.
A.N. Sial et al.r Lithos 46 (1999) 367–392
373
374
A.N. Sial et al.r Lithos 46 (1999) 367–392
Palaeozoic times, and of continental extension, is the
boundary between the Cumbres de Calchaquies in
the northeast and the Sierra de Aconquija in the
southwest. Along this megafracture, a group of late
to post-tectonic mEp-bearing calc-alkalic granitoids
˜ ˜
ŽEl Infiernillo, Loma Pelada, Nunorco
Grande, La
Angostura and El Indio; Fig. 3. was emplaced into
low- to medium-grade metamorphic rocks. Another
mEp-bearing pluton ŽCafayate pluton., similar in age
and composition, is found to the north of the Tafi
Megafracture ŽRapela, 1976; Rapela and Shaw, 1979;
Rapela et al., 1982..
The Infiernillo pluton is essentially homogeneous,
and is composed of granular tonalite cut by a few
dykes of two-mica granodiorite, with mEp and
˜ ˜
opaques. The Loma Pelada and Nunorco
Grande
plutons, although separated by intervening metamorphic rocks, are perhaps part of a single pluton composed of biotite–muscovite granodiorite, and muscovite granite, with tourmaline-bearing pegmatitic
dykes. The Loma Pelada, Infiernillo and Cafayate
plutons were emplaced at relatively shallow depths,
developing thermal contact aureoles in the surrounding metasedimentary rocks containing muscovite,
staurolite and cordierite. La Angostura tonalite and
El Indio granodiorite plutons were emplaced and
crystallized at a late to post-tectonic stage, forming a
typical calc-alkalic series.
mEp has been recognized in the following plutons
of the FGP: Cerro Toro, Paganzo, Cerro Blanco, San
˜ ˜
Agustin, Narvaez, Nunorco–Sanogasta,
Copacabana
˜
and Paiman. The granitoid plutons of the FGP intruded Neoproterozoic–Early Cambrian metamorphic rocks and have been dated between 500 and 400
Ma ŽRapela et al., 1991; Toselli et al., 1997..
˜ ˜
The Narvaez, Copacabana, Paiman and Nunorco–
Sanogasta
plutons intruded rather low-grade meta˜
morphic rocks, locally developing andalusite and
cordierite hornfels. The Cerro Toro, Cerro Blanco
and Paganzo plutons, however, intruded muscovite–
cordierite–sillimanite gneisses and migmatites, suggesting somewhat deeper emplacement.
The metaluminous characteristics of the mEpbearing plutons in the FGP, where muscovite is
virtually absent, contrasts with the peraluminous
character of the mEp-bearing granitoids in the Pampean Ranges. Whole-rock chemical data for mEpbearing plutons in the FGP and Tafi Megafracture
are described by Toselli et al. Ž1997.. All belong to
the calc-alkalic series.
2.3. Chile
Six calc-alkalic, metaluminous, mEp-bearing
tonalites and granodiorites have been identified in
the Carboniferous Southern Coastal batholith and
High Andes Cordillera of central Chile, and, further
south in the Cretaceous to Tertiary North Patagonian
batholith ŽFig. 4c.. The Carboniferous plutons are
petrographically similar to mEp-bearing granitoids in
NE Brazil, except that the amount of mEp is lower
and secondary epidote is commonly observed. They
belong to the calc-alkalic series and a review and
detailed discussion on Pre-Andean to Andean granitoids, including the plutons in this, study may be
found in Parada Ž1990..
Small amounts of mEp are present in the Carboniferous granitoids. They occur within plagioclase
crystals or partially surrounded by biotite crystals.
Zoned allanite cores in epidote are also observed in
some Carboniferous granites of the High Andes
Cordillera. In the North Patagonian batholith, amphibole is commonly replaced by epidote of ambiguous
origin in the 10 Ma-old Queulat quartz diorite while
small epidote grains, included in hornblende, show
optical and textural characteristics suggestive of an
igneous origin.
3. Amphibole barometry
It has been demonstrated that total Al content of
hornblende in intermediate calc-alkalic rocks varies
linearly with crystallization pressure ŽHammarstrom
and Zen, 1986. and an empirical barometric equation
was proposed. The empirical calibration of this
barometer is essentially identical to that of Hollister
et al. Ž1987. who reduced the 3 kbar error to 1 kbar.
Johnson and Rutherford Ž1989. and Thomas and
Ernst Ž1990. added experimental calibrations to this
barometer. Results differ slightly from empirical calibrations and uncertainties were reduced to 0.5 kbar.
Schmidt Ž1992. recalibrated this barometer using
epidote-bearing tonalite and made it applicable up to
A.N. Sial et al.r Lithos 46 (1999) 367–392
13 kbar, while Johnson and Rutherford Ž1989. used
CO 2 –H 2 O fluid, Schmidt used an H 2 O-saturated
fluid.
The presence of mEp in calc-alkalic plutons is
indicative of low CO 2 activity ŽGhent et al., 1991.
and, in principle therefore, the calibration by Schmidt
would be expected to be the most appropriate for
mEp-bearing plutons. However, other factors controlling the chemistry of hornblende should be taken
into account as pointed by Anderson and Smith
Ž1995. and Anderson Ž1996.. According to these
authors, temperature, f H 2 O and total pressure have
an important influence on mafic silicate mineral
chemistry, although f O 2 is the main controlling
factor. These authors demonstrated that this barometer fails by yielding elevated pressures for low-f O 2
plutons with iron-rich hornblende coexisting with the
full barometric assemblage. With increasing f O 2 ,
the FerŽFe q Mg. ratio for hornblende and biotite
markedly decreases, independent of the FerMg ratio
of the whole rock ŽAnderson and Smith, 1995; Anderson, 1996..
The calibration of the Al-in-hornblende barometer
by Anderson and Smith Ž1995. has been used here
only with the appropriate mineral assemblage to
buffer Al-in-hornblende and when the FerŽFe q Mg.
ratios for hornblende are in the range 0.40–0.65,
indicating high f O 2 . Representative microprobe
analyses of hornblende rims from the main plutons
under consideration are shown in Table 1. In each
pluton, at least three grains of hornblende were
analyzed.
3.1. NE Brazil
Pressure estimates for mEp-bearing calc-alkalic
granitoids in the CST, using the Al-in-hornblende
geobarometer by Anderson and Smith Ž1995., are in
the 5–8.5 kbar range ŽAl t varies from 1.81 to 2.48.,
including clinopyroxene-bearing plutons ŽFig. 5..
Unfortunately, no regional P–T data are available
for metasedimentary rocks near mEp-bearing plutons
in this terrane. The presence of the assemblage kyanite–staurolite–garnet in contact aureoles of two plutons, however, seems to confirm the Al-in-hornblende barometry.
375
mEp-bearing calc-alkalic plutons in this terrane
share similar petrographic and mineralogical characteristics and probably experienced similar crystallization histories. Therefore, liquidus temperatures at the
depth of emplacement of these CST plutons probably
varied very little from pluton to pluton. In this way,
these plutons, offer a good opportunity to test the
application of the zircon saturation method ŽWatson
and Harrison, 1983; Watson, 1987. and of estimating
liquidus temperatures. As long as most zircons are
not restitic, xenocrystic or cumulate in origin, and
are early-crystallized, these calculations provide the
only information on minimum liquidus temperatures
that may be comparable to conditions of melt formation.
Liquidus temperature estimates obtained for CST
mEp-bearing plutons Ž785–8508C., assuming that all
the requirements of this method are satisfied, when
plotted against corresponding Al-in-hornblende pressure estimates ŽFig. 6. show a reasonable alignment.
As the magmas under consideration were relatively
hydrated, these temperature estimates appear to be
realistic.
In the calc-alkalic mEp-bearing plutons in the
MT, the Al-in-hornblende method yielded pressure
estimates of 5 and 6 kbar. The metamorphic assemblages in the host metagreywackes yield poorly-constrained pressure estimates that suggest maximum
pressures around 5.5 kbar ŽMcReath et al., in press..
In the APT, amphibole crystallization pressure
estimates for the mEp-bearing granitoids are in the
5–8 kbar range ŽPalmeira trondhjemitic tonalite,
Teixeira shoshonitic monzogranite, high-K calc-alkalic Brejinho, Tavares, Conceiçao
˜ das Creoulas and
Caldeirao
˜ Encantado plutons.. In all of the studied
plutons of the APT, liquidus temperature estimates
by the Zr saturation method, are in the 785–8508C
range, similar to the temperature range found in the
CST and MT mEp-bearing plutons ŽFig. 6..
Al-in-hornblende from amphiboles from four
calc-alkalic and one high-K calc-alkalic mEp-bearing
plutons in the ST, yielded pressures in the 3.5–4.5
kbar range. Pressures obtained from hornblendes of
the Sao
˜ Rafael pluton, one of the largest mEp-bearing
granitoids in this terrane, are in agreement with
pressure estimates for the nearby metamorphic country rocks of the Serido´ Group Ž3–4 kbar; Lima,
1987..
45.66
0.57
8.32
17.91
0.41
11.05
11.08
1.20
0.97
97.37
SiO 2
TiO 2
Al 2 O 3
FeO
MnO
MgO
CaO
Na 2 O
K2O
Total
44.08
0.68
12.08
13.99
0.35
10.91
11.40
1.73
1.50
96.72
Number of cations on the basis of 23 oxygens
Si
6.597
6.956
6.510
Al IV
1.403
1.044
1.490
8.000
8.000
8.000
Ti
0.077
0.057
0.090
AlVI
0.736
0.631
0.740
Fe 2q
1.750
1.629
2.280
Mn
0.044
0.041
0.040
Mg
2.433
2.681
1.960
5.040
5.039
5.110
Ca
1.828
1.804
1.790
Na
0.501
0.395
0.480
K
0.286
0.207
0.260
2.615
2.400
2.530
44.33
0.66
8.44
18.15
0.37
11.25
11.65
1.32
0.95
97.24
11
6.350
1.650
8.000
0.140
0.590
2.290
0.000
2.000
5.020
2.060
0.290
0.280
2.630
47.56
0.52
9.72
13.32
0.33
12.30
11.51
1.40
1.11
96.66
15
3
Point
3
KSR-36
Sample
MBV-20
Boa Ventura
Sao
˜ Rafael
Pluton
KSR-4
Cachoeirinha–Salgueiro
Serido´
Terrane
NE Brazil
6.460
1.540
8.000
0.150
0.940
1.760
0.040
2.290
5.180
1.630
0.440
0.170
2.240
44.00
0.80
12.90
18.60
0.30
9.00
11.40
1.70
1.40
100.17
An
SER-45
6.530
1.470
8.000
0.110
0.880
2.350
0.030
1.830
5.200
1.800
0.460
0.300
2.560
42.00
1.25
12.55
18.20
0.01
8.90
12.74
1.00
1.45
97.99
An
SER-47
St. Antonio Creek
6.508
1.492
8.000
0.122
0.584
2.205
0.045
1.923
4.889
2.062
0.426
0.332
2.820
44.80
1.40
14.60
14.60
0.35
10.70
10.60
1.60
0.90
99.22
An
SER-77
Penaforte
6.507
1.493
8.000
0.077
0.684
2.168
0.053
1.862
4.844
2.090
0.431
0.331
2.852
43.50
1.00
12.40
18.70
0.25
8.20
11.20
1.60
1.60
98.21
An
SER-86
Table 1
Representative electron microprobe analyses of amphibole rims from magmatic epidote-bearing granitoids in this study
6.860
1.140
8.000
0.140
0.350
2.280
0.050
2.510
5.330
1.830
0.330
0.170
2.330
42.67
1.06
11.55
17.29
0.35
8.46
12.62
1.44
1.71
97.15
2
PB-33
6.740
1.260
8.000
0.150
0.250
2.200
0.050
2.550
5.200
1.760
0.390
0.180
2.330
42.33
0.66
12.02
16.86
0.41
8.13
12.69
1.45
1.69
96.24
3
Pedra Branca
Alto Pajeu
´
6.380
1.620
8.000
0.040
0.660
2.520
0.000
1.890
5.110
2.080
0.150
0.260
2.490
42.30
0.40
12.80
20.00
0.00
8.40
12.90
0.55
1.40
98.77
A
ITIM-50
Brejinho
6.370
1.630
8.000
0.050
0.810
2.540
0.000
1.740
5.140
1.980
0.130
0.260
2.370
42.50
0.45
13.80
20.30
0.00
7.80
12.35
0.45
1.40
99.04
B
6.419
1.581
8.000
0.068
0.501
2.667
0.000
1.761
4.997
1.818
0.380
2.201
2.281
40.98
0.58
11.29
21.29
0.46
7.54
11.53
1.26
1.59
96.58
1R
TV-2
6.795
1.250
8.000
0.046
0.429
2.311
0.000
2.206
4.992
1.894
0.387
44.90
0.40
9.17
18.63
0.46
9.78
11.93
1.32
1.06
97.65
2R
TV-7
Tavares
6.400
1.600
8.000
0.092
0.593
2.714
0.053
1.701
5.153
1.890
0.393
0.340
2.623
42.01
0.80
12.22
21.03
0.41
7.49
11.58
1.23
1.75
96.77
24R
RCC-04
Crioulas
33R
6.349
1.651
8.000
0.076
0.687
2.541
0.058
1.634
4.996
1.920
0.355
0.382
2.657
40.95
0.65
12.81
20.51
0.44
7.07
11.56
1.18
1.44
96.61
376
A.N. Sial et al.r Lithos 46 (1999) 367–392
43.95
0.91
10.8
14.61
0.44
9.59
11.48
1.37
1.38
97.53
All analyses are in wt.% and all are for rims.
a
From Rossi de Toselli et al. Ž1991 ..
Number of cations on the basis of 23 oxygens
Si
6.643
6.705
6.634
Al IV
1.357
1.295
1.366
8.000
8.000
8.000
Ti
0.150
0.177
0.103
VI
Al
0.376
0.395
0.554
Fe 2q
2.029
2.082
2.207
Mn
0.045
0.048
0.056
Mg
2.516
2.361
2.158
5.116
5.063
5.078
Ca
1.850
1.845
1.857
Na
0.449
0.388
0.362
K
0.247
0.217
0.266
2.546
2.450
2.485
44.92
1.58
9.62
16.68
0.38
10.61
11.54
1.61
1.14
98.08
6.568
1.435
8.000
0.130
0.565
2.240
0.049
2.115
5.099
1.875
0.322
0.293
2.490
43.18
1.14
11.17
17.61
0.38
9.33
11.51
1.16
1.51
96.99
05-R2
6.475
1.525
8.000
0.102
0.492
2.300
0.107
2.212
5.213
1.927
0.347
0.185
2.459
42.92
0.91
11.32
18.22
0.82
9.86
11.91
1.20
0.99
98.15
B
6.433
1.567
8.000
0.090
0.612
2.398
0.074
2.112
5.286
1.844
0.323
0.173
2.340
42.55
0.83
12.24
18.99
0.63
9.37
11.40
1.12
0.95
98.08
B
6.737
1.263
8.000
0.100
0.364
2.276
0.127
2.390
5.257
1.828
0.337
0.172
2.337
44.32
0.94
9.09
17.93
1.04
10.55
11.26
1.15
0.93
97.21
B
6.578
1.421
8.000
0.191
0.273
2.560
0.109
2.050
5.183
1.904
0.346
0.218
2.468
43.58
1.72
9.51
20.22
0.90
9.09
11.74
1.21
1.15
98.92
B
5003
6.520
1.480
8.000
0.167
0.350
2.740
0.102
1.857
5.216
1.848
0.390
0.240
2.478
42.22
1.45
10.02
21.20
0.83
8.07
11.20
1.32
1.22
97.53
B
6.380
1.620
8.000
0.130
0.410
2.862
0.102
1.779
5.283
1.946
0.316
0.242
2.504
41.19
1.15
11.14
21.83
0.83
7.71
11.57
1.11
1.29
97.82
B
4299
6.834
1.166
8.000
0.095
0.488
2.283
0.029
2.205
5.100
1.899
0.291
0.172
2.362
45.60
0.84
9.37
18.22
0.23
9.87
12.12
0.75
0.90
97.90
1B
18
44.25
1.33
9.8
16.16
0.35
11.24
11.5
1.64
1.29
97.56
05-R1
4974
4943
SiO 2
TiO 2
Al 2 O 3
FeO
MnO
MgO
CaO
Na 2 O
K2O
Total
R-2
4757
R-1
4761
Point
HJCS
GN-04
Sample
Sierra de Paganzo a
Guanta
Cerro Blanco a
Cerro Toro a
Coronel Joao
˜ Sa´
Gloria Norte
Pluton
Chile
High Andes
Argentina
Famatina Geological System
NE Brazil
Macurure´
Terrane
Table 1 Žcontinued .
6.749
1.251
8.000
0.087
0.398
2.219
0.022
2.408
5.134
1.847
0.222
0.173
2.244
44.84
0.77
9.30
17.63
0.17
10.73
12.26
0.76
0.90
97.40
3B
31
6.829
1.171
8.000
0.127
0.364
2.102
0.061
2.459
5.113
1.922
0.325
0.155
2.402
45.58
1.13
8.70
16.77
0.48
11.01
11.97
1.12
0.81
97.57
1B
SD-36
6.886
1.114
8.000
0.058
0.317
2.188
0.065
2.516
5.144
1.929
0.352
0.139
2.420
45.50
0.51
8.03
17.29
0.51
11.15
11.90
1.20
0.72
99.21
2B
SD-40
6.781
1.219
8.000
0.113
0.480
2.071
0.053
2.454
5.023
1.875
0.331
0.086
2.292
45.51
1.00
9.64
16.55
0.42
11.00
11.69
1.14
0.45
97.40
1B
CQ-48-B
Cuesta Queulat
6.838
1.162
8.000
0.115
0.597
2.093
0.046
2.308
5.046
1.819
0.256
0.091
2.166
46.19
1.03
10.09
16.94
0.37
10.46
11.47
0.95
0.48
97.98
3B
CQ-5638
South Coastal batholiths North Patagonia batholiths
Santo Domingo
A.N. Sial et al.r Lithos 46 (1999) 367–392
377
378
A.N. Sial et al.r Lithos 46 (1999) 367–392
Fig. 5. P–T plot for mEp-bearing granitoids, including appropriate P and T uncertainties, in NE Brazil, NW Argentina and Chile.
Pressures have been estimated by the Al-in-hornblende ŽAnderson and Smith, 1995 calibration. barometer and temperatures by
plagioclase–hornblende pairs Žthermometer of Holland and Blundy, 1994.. Dashed line at 5 kbar is for minimum P of epidote stability in
water-saturated tonalitic melts under f O 2 buffered by NNO. Epidote compositional ranges Žmol% Ps. have been added for comparison with
corresponding pressure ranges.
A.N. Sial et al.r Lithos 46 (1999) 367–392
379
in the Elqui superunit.. The FerŽFe q Mg. ratios in
hornblendes are in the 0.43–0.50 range.
In Fig. 6, pressure estimates obtained by hornblende barometry in this study have been plotted
against temperatures estimated by the revised calibration of the hornblende–plagioclase thermometer
ŽHolland and Blundy, 1994.. Plagioclase–hornblende
pairs from Chilean and Argentinian mEp-bearing
granitoids yielded similar temperature ranges,
whereas some more mafic granitoids in NE Brazil
display a higher temperature range. Plutons in NE
Brazil, except for those in the ST, were emplaced at
pressures equivalent to, or slightly higher than, those
in the FGP in Argentina, whereas Chilean mEpbearing plutons were emplaced at shallower depths.
Fig. 6. ŽA. P – T plot for mEp-bearing granitoids in NE Brazil;
ŽB. for mEp-bearing granitoids in Argentina ŽFGP. and Chile.
Curve 1: temperatures obtained from zircon saturation equation ŽT
Ž8C. sy273q12,900r17.18-lnŽZr.; Watson, 1987., and pressures by Al-in-hornblende barometric calibration by Schmidt
Ž1992.. Curve 2: melting curve for excess H 2 O granodiorite
composition ŽPiwinskii and Wyllie, 1968.. The symbol Ž). is for
CST and MT mEp-bearing calc-alkalic granitoids, while symbol
Ž`. is for APT high-K calc-alkalic granitoids.
4. Epidote chemistry
More than 100 microprobe analyses of epidote
were performed in this study. Cores and rims of
three grains per pluton were usually analyzed. Compositional ranges are shown in Fig. 7 and representative core and rim analyses in Table 2.
4.1. NE Brazil
3.2. NW Argentina and Chile
Pressures of amphibole crystallization have been
calculated for some calc-alkalic granitoid plutons in
the FGP that intrude syntectonically intermediate to
high-grade cordierite–sillimanite-bearing gneissesr
mig-matites; namely the Cerro Toro, Cerro Blanco
and Sierra de Paganzo tonalites ŽRossi de Toselli et
al., 1991.. Calcic hornblendes in these plutons show
Al in the 1.60–2.20 range corresponding to pressures
of solidification of 6.5–7.5 kbar ŽCerro Toro pluton.,
4.4 kbar ŽCerro Blanco pluton. and 5.6 kbar ŽSierra
de Paganzo pluton..
All hornblendes from Chilean granitoids analyzed
in this study, are Mg-hornblende. Those from the
Santo Domingo pluton in the Southern Coastal
batholith yielded solidification pressures around 4.5
kbar, between 5.5 and 6 kbar in the Late Tertiary
granitoids on the North Patagonian batholith, and
between 4.5 and 5.5 kbar in the High Andes
Cordillera batholith ŽGuanta and Pisco-Elqui plutons
Microprobe data indicate that the mole percent Ps
of euhedral mEp in the high-K calc-alkalic Sao
˜
Rafael batholith in the ST lies in a narrow range
ŽPs 27 – 29 . with some variation of Al and Fe contents
from core to margin, indicated by the data in Table
2. The Ps contents ŽPs 25 – 29 . are within the range
reported to be typical for mEp ŽTulloch, 1979; Vyhnal et al., 1991.. Galindo Ž1993. reported epidotes in
the Prado pluton with a narrow compositional range
ŽPs 28 – 29 ., equivalent to that observed in epidotes of
the Sao
˜ Rafael pluton.
mEp in calc-alkalic plutons in the CST has Ps
contents between 20 and 24, within the range of
epidote phenocrysts ŽPs 19 – 24 . in high-K calc-alkalic
dykes of the of the Front Range of Colorado ŽDawes
and Evans, 1991. which are considered to be unequivocally mEp. Some examples described by
Rogers Ž1988., Owen Ž1991. and Farrow and Barr
Ž1992., also lie in this range. Typically, the CST
mEp have lower proportions of the Ps component,
380
A.N. Sial et al.r Lithos 46 (1999) 367–392
Fig. 7. Histograms of mole percent Žmol%. Ps in magmatic epidotes from NE Brazil, NW Argentina and Chile. The compositional ranges of
epidote from alteration of plagioclase and biotite are from Tulloch Ž1979.. Johnston and Wyllie Ž1988, Fig. 5, p. 42. observed values of
20–24, 28 mol% Ps for igneous epidote in rocks and 26–30 mol% Ps, in experiments.
higher Si, Al, Ca, Ti and lower Fe contents than
those of the ST.
mEp from the shoshonitic Teixeira pluton and
trondhjemitic Palmeira pluton, in the APT, show a
narrow compositional variation ŽPs 25 – 28 .. Values for
the trondhjemitic Serrita pluton in the CST are lower
ŽPs around 21..
Ps contents of high-K calc-alkalic plutons in the
APT show broader compositional variation ŽPs 21 – 29 ..
In the Conceiçao
˜ das Creoulas pluton, mEp grains
are usually zoned, with the Feq3 content increasing
from core to rim. Ps content varies with epidote
textural types in the following way: Ža. those included in feldspars exhibit compositions around Ps 21 ,
at their rims; Žb. those surrounding allanite have rim
composition of Ps 25 – 27 , and Žc. those rimmed by
biotite display rim compositions of Ps 21 – 23 .
Epidotes in the ST plutons crystallized under a
different oxygen fugacity buffer than epidotes in the
CST plutons. Compositions for this mineral in grani-
37.54
0.09
22.16
0.00
0.02
23.34
0.10
13.85
n.d.
0.00
97.11
SiO 2
TiO 2
Al 2 O 3
Cr 2 O 3
MgO
CaO
MnO
FeO
Na 2 O
K2O
Total
38.44
0.20
24.33
0.05
0.05
23.87
0.22
10.38
0.03
0.01
97.60
38.12
0.15
23.80
0.05
0.04
23.90
0.19
10.70
0.00
0.01
96.96
Number of cations on the basis of 25 oxygens
Si
3.102
3.104
3.025
3.029
Ti
0.13
0.009
0.006
0.007
Al
2.314
2.284
2.235
2.231
Cr
0.003
0.003
0.001
0.009
Mg
0.005
0.15
0.008
0.013
Ca
2.067
2.086
2.035
2.045
Mn
0.14
0.013
0.006
0.005
Fe
0.700
0.725
0.686
0.663
Na
0.005
0.000
–
–
K
0.000
0.001
0.000
0.000
Ps
23
24
23
23
38.00
0.05
22.02
0.00
0.00
23.22
0.22
13.75
n.d.
0.00
97.29
Core
Rim
Core
Point
Rim
SR-3
Sample
MBV-23
Sao
˜ Rafael a
Pluton
2.903
0.005
2.020
0.000
0.002
1.934
0.007
0.807
–
0.000
28
37.97
0.10
23.82
0.02
0.07
23.84
0.09
11.45
0.00
0.00
97.36
Core
E-57
Emas
Cachoeirinha–Salgueiro
Boa Ventura
Serido´
Terrane
NE Brazil
Table 2
Representative electron microprobe analyses of epidote in this study
2.929
0.003
2.001
0.000
0.003
1.918
0.012
0.799
–
0.000
28
38.22
0.12
23.91
0.11
0.15
24.08
0.07
11.13
0.00
0.01
97.80
Rim
3.004
–
2.366
–
0.002
1.999
–
0.626
–
0.00
21
38.38
–
25.67
n.d.
0.02
23.84
n.d.
9.57
n.d.
0.00
97.48
Core
TV-2.1
Tavares
Alto Pajeu
´
3.029
–
2.184
–
0.000
2.017
–
0.762
–
0.000
27
38.82
–
23.77
n.d.
0.02
24.45
n.d.
11.69
n.d.
0.00
98.55
Rim
3.030
–
2.333
–
0.006
1.993
–
0.625
–
–
22
38.92
0.00
25.02
0.02
0.14
24.17
n.d.
11.22
n.d.
n.d.
98.37
Core
RCC-16-A
Crioulas
2.967
–
2.331
–
0.000
1.988
–
0.700
–
–
24
37.49
0.13
25.01
0.00
0.00
23.45
n.d.
11.76
n.d.
n.d.
98.03
Rim
3.011
0.005
2.162
0.003
0.000
1.895
0.014
0.856
0.000
0.000
28
38.15
0.09
23.26
0.07
0.00
22.42
0.47
12.98
0.00
0.00
97.42
Core
P-6
Palmeira
2.981
0.003
2.229
0.001
0.000
1.967
0.012
0.799
0.000
0.000
27
38.11
0.02
24.2
0.03
0.00
23.47
0.25
12.23
0.01
0.00
98.32
Rim
3.018
–
2.224
–
0.001
1.956
–
0.751
0.000
0.000
27
38.34
0.11
23.99
0.03
0.01
23.19
0.34
11.43
0.00
0.00
97.44
Core
TX-12
Teixeira
2.986
–
2.265
–
0.000
1.973
–
0.764
0.000
0.000
24
37.73
0.01
24.30
0.00
0.00
23.27
0.00
11.56
0.04
0.01
96.87
Rim
Macurure´
3.026
0.007
2.324
0.000
0.011
1.992
0.000
0.630
–
–
21
38.29
0.12
24.97
0.00
0.09
2.53
0.00
10.55
0.03
0.00
97.58
Core
GN-4
3.031
0.007
2.302
0.005
0.014
2.004
0.003
0.620
–
–
21
38.35
0.12
24.73
0.08
0.12
23.66
0.04
10.49
0.03
0.00
97.59
Rim
Gloria Norte
2.881
–
2.328
–
0.003
1.902
0.000
0.535
–
–
20
38.47
0.14
26.4
0.01
0.03
23.71
0.18
8.55
0.00
0.00
97.53
Core
H-11
2.871
–
2.871
–
0.003
1.876
0.000
0.530
–
–
18
38.23
0.20
26.68
0.04
0.03
23.32
0.12
8.45
0.01
0.01
97.10
Rim
Cel. Joao
˜ Sa´
A.N. Sial et al.r Lithos 46 (1999) 367–392
381
Infiernillo
CAF
Core
40.52
0.09
22.44
0.06
0.10
22.22
0.38
10.99
0.00
0.00
96.80
Sample
Point
SiO 2
TiO 2
Al 2 O 3
Cr 2 O 3
MgO
CaO
MnO
FeO
Na 2 O
K2O
Total
37.49
0.15
23.01
0.02
0.00
23.10
0.66
12.01
0.19
0.02
96.53
Rim
47-2C
38.08
0.05
23.73
0.00
0.06
23.71
0.38
11.41
0.16
0.00
97.52
Core
Analyses in wt.%.
Total Fe measured as FeO.
a
From Galindo Ž1993 ..
b
From Belen Perez et al. Ž1996 ..
Number of cations on the basis of 25 oxygens
Si
3.214
3.024
3.031
Ti
0.005
0.009
0.003
Al
2.096
2.186
2.224
Cr
0.004
0.001
0.000
Mg
0.012
0.000
0.007
Ca
1.888
1.995
2.022
Mn
0.025
0.045
0.026
Fe
0.655
0.728
0.683
Na
0.000
0.000
0.023
K
0.030
0.002
0.000
Ps
24
24
23
Cafayate
Pluton
Rim
3.031
0.012
2.207
0.009
0.005
2.004
0.027
0.696
0.011
0.000
24
38.30
0.20
23.68
0.15
0.04
23.63
0.04
11.69
0.07
0.00
97.80
3.086
0.008
2.156
0.000
0.013
1.995
0.030
0.775
0.028
0.009
27
37.47
0.13
22.74
0.00
0.11
23.13
0.44
12.80
0.18
0.00
97.00
Core
CT-40
Cerro Toro
Rim
Sierra Chica de Cordobab
3.036
0.007
2.141
0.007
0.007
1.994
0.025
0.770
0.000
0.002
27
38.40
0.12
22.99
0.12
0.06
23.54
0.38
12.95
0.05
0.02
97.64
EP-3
3.020
0.010
2.130
–
0.000
1.980
0.020
0.820
–
–
28
37.78
0.13
22.58
–
0.02
23.13
0.34
13.53
–
–
97.73
Core
3.000
0.010
2.160
–
0.010
1.980
0.010
0.810
–
–
27
37.69
0.12
23.03
–
0.05
23.45
0.26
13.48
–
–
97.77
Rim
3.018
0.001
2.239
0.003
0.006
2.005
0.015
0.729
–
–
24
38.04
0.02
23.96
0.04
0.05
23.59
0.22
11.80
0.19
0.00
97.91
Core
GUA
Guanta
Chile
High Andes
Tafi Megafracture
Famatina
NW Argentina
Table 2 Žcontinued .
3.046
0.000
2.224
0.000
0.032
1.972
0.018
0.718
–
–
24
38.22
0.00
2370
0.00
0.27
23.10
0.27
11.47
0.20
0.00
97.23
Rim
Southern Coastal batholith
3.011
0.001
2.215
0.000
0.011
2.037
0.015
0.722
0.006
0.000
24
37.67
0.02
23.53
0.00
0.09
23.78
0.22
12.02
0.04
0.00
97.33
Core
SD-1
3.021
0.011
2.203
0.000
0.013
2.001
0.013
0.733
0.00
0.002
24
38.12
0.18
23.60
0.00
0.11
23.57
0.20
18.30
0.00
0.02
98.08
Rim
Santo Domingo
North Patagonian batholith
3.031
0.002
2.201
0.004
0.002
2.028
0.011
0.718
0.006
0.000
24
38.05
0.04
23.47
0.06
0.02
23.7
0.16
11.93
0.04
0.00
97.54
Core
CQ
3.003
0.000
2.267
0.000
0.000
2.045
0.014
0.681
0.019
0.000
23
37.58
0.00
24.09
0.00
0.00
23.58
0.20
11.34
0.12
0.00
97.21
Rim
Cuesta de Queulat
382
A.N. Sial et al.r Lithos 46 (1999) 367–392
A.N. Sial et al.r Lithos 46 (1999) 367–392
toids in the ST lie between the Ps 25 and Ps 33 ŽNNO
and HM buffer curves, respectively, according to
Liou, 1973.. In the CST granitoids, epidote crystallized under f O 2 close to the NNO buffer curve.
In the Macurure´ terrane, mEp in the Gloria Norte
and Coronel Joao
˜ Sa´ plutons displays compositions
in the Ps 20 – 22 and Ps 19 – 25 ranges, respectively.
4.2. NW Argentina
Compositions of mEp in the Ps 23 – 26 range are
observed in plutons of the Tafi Megafracture ŽInfiernillo and Cafayate plutons.. In the FGP, epidotes
from the Cerro Toro pluton display compositions
around Ps 26 while Belen Perez et al. Ž1996. reported
compositions in the 26–28 mol% Ps range for epidotes in the Sierra Chica de Cordoba pluton, in
which up to 3% modal epidote is present. All epidote
grains analysed in this study have less than 0.20% by
weight of TiO 2 , and are usually chemically zoned
with rims slightly Fe, Ca enriched in relation to their
cores.
4.3. Chile
mEp from the Guanta, Las Terneras and Pisco
Elqui plutons in the Elqui superunit of the High
Andes Cordillera have compositions in the Ps 20 to
Ps 24 range, while the Santo Domingo pluton have
compositions varying around Ps 24 . Epidote related to
hornblende, in the Tertiary Cuesta de Queulat pluton,
has a compositional range from Ps 20 to Ps 24 .
5. Magnetic susceptibility
Ishihara Ž1977. proposed that granites can be
subdivided into magnetite series Žhigh f O 2 . and
ilmenite-series Žlow f O 2 . with the boundary approximately between the NNO and QFM buffers. The
magnetite content of rocks is easily determined by
magnetic susceptibility ŽMS. measurements which is
a qualitative means of estimating the oxygen fugacity of granitoids. In this study, the digital kappameter
KT-5, a field portable MS meter was used; measurements are reported in SI units. The MS data obtained
383
from mEp-bearing granitoids from NE Brazil, Argentina and Chile are presented in Fig. 8.
Almost all Neoproterozoic mEp-bearing plutons
in NE Brazil, Early Palaeozoic equivalent granitoids
in Argentina ŽInfiernillo, Loma Pelada and Anguinan
plutons. and Late Palaeozoic in Chile ŽGuanta and
Las Terneras., in which opaque phases are almost
absent, low MS Žf 0.3 = 10y3 SI. was recorded. All
of these plutons correspond, in terms of MS, to
ilmenite-series granitoids of Ishihara Ž1977. ŽMS
values - 3 = 10y3 SI, the limit between ilmeniteand magnetite-series granitoids of Takahashi et al.,
1980.. In contrast, granitoids from two plutons in
Chile ŽPisco Elqui and Santo Domingo. and three in
˜ ˜
Argentina ŽEl Indio, Nunorco
and Cerro Toro. contain some rectangular magnetite and have much
higher MS values Ž3 to 10 = 10y3 SI., departing
from values obtained in natural and experimental
mEp-bearing granitoids. In granitoids from the Tertiary Queulat pluton in Chile primary magnetite is
found in greater amounts; these having the highest
MS values Ž40 to 50 = 10y3 SI..
Magnetite-seriesrilmenite-series volcanic rocks
increase drastically from the Mesozoic to Recent in
Japan ŽIshihara, 1977.. Schmidt and Thompson
Ž1996. concluded from experiments that magnetite is
significantly more abundant in epidote-free than in
epidote-bearing granitoid intrusions. From these observations and this study, it can be inferred that mEp
often occurs in Precambrian to Palaeozoic ilmeniteseries granitoids. Its occurrence in magnetite-series
granitoids, with some exceptions, is more restricted
to Mesozoic to Tertiary granitoids, usually in lower
amounts as suggested by the experiments.
In this study, most epidote-bearing granitoids apparently belong to the ilmenite-series granitoids, and
are therefore of low oxygen fugacity magmas. However, epidote and hornblende compositions demonstrate that oxygen fugacity was higher Žbetween NNO
and HM buffers. than that required for the ilmeniteseries granitoids Žbetween NNO and QFM buffers..
6. Upward magma migration
Epidote textural relationships may provide a clue
to understanding upward magma transport ŽBrandon
384
A.N. Sial et al.r Lithos 46 (1999) 367–392
Fig. 8. Histograms of magnetic susceptibility ŽMS. of some mEp-bearing granitoids in NE Brazil, NW Argentina and Chile in this study.
There are 12 readings per representative outcrop per pluton.
et al., 1996.. To illustrate this, mEp-bearing plutons
from the same terrane ŽAPT. in NE Brazil, in which
epidote shares similar textural relationships, have
been chosen to apply the parameters described by
A.N. Sial et al.r Lithos 46 (1999) 367–392
Brandon et al. Ž1996. to estimate relative rate of
epidote dissolution in relation to upward magma
migration.
These plutons are elongate in a SW–NE direction
and they probably filled fractures opened during the
development of the Brasiliano orogeny in this region.
This situation seems to support emplacement by
dyking rather than by diapirism. To test this fieldbased assumption with possible conclusions to be
drawn from epidote textural relationships, four different textural situations common to most of these
plutons are shown in Fig. 9.
In Fig. 9a, euhedral mEp has a chemically zoned
allanite core and is wholly rimmed by biotite, while
in Fig. 9b, euhedral mEp with an allanite core is
wholly rimmed by K-feldspar. In Fig. 9c, subhedral
385
epidote is included in plagioclase, whereas in Fig.
9d, mEp was partially resorbed by the host magma in
that portion not rimmed by biotite.
In relation to Fig. 9a and b, mEp seems to have
survived dissolution by the host magma because it
was armoured by biotite Žexamples where biotite
armour is, in turn, within interstices formed by Kfeldspar aggregates are common. or by K-feldspar.
In both these examples, not only very rapid upward
transport rate has been responsible for the epidote
surviving dissolution, but probably rapid near-solidus
of K-feldspar growth Žfaster than epidote dissolution
rate. contributed.
In relation to Fig. 9c and d, the magma transport
rate was probably rapid enough to guarantee epidote
survival to complete dissolution, supporting dyking
Fig. 9. Magmatic epidote textural relationships common to all of the studied high-K calc-alkalic plutons in the Alto Pajeu´ terrane, NE
Brazil. Ža. Epidote armoured by biotite; Žb. armoured by aggregates of K-feldspar; Žc. partially resorpted, included in plagioclase and Žd.
partially armoured by biotite, partially resorpted. Abbreviations are: al s allanite, bi s biotite, ep s epidote, K-spars K-feldspar, plag s
plagioclase and qz s quartz. Dashed lines in Žc. and Žd. are an attempt to reconstruct original shape of epidote crystals indicating how much
of these crystals have been dissolved by the host magma.
386
A.N. Sial et al.r Lithos 46 (1999) 367–392
as the probable mechanism of upward magma migration for this and the other mEp-bearing plutons in
this area where similar epidote textural relationships
are present.
Upward migration rates of host magmas can be
estimated wherever partially dissolved epidote is armoured by plagioclase Žepidote and plagioclase can
coexist around 10 kbar in tonalitic magmas as experimentally demonstrated by Schmidt and Thompson
Ž1996, Fig. 2, p. 467. and epidote has grown simultaneously with K-feldspar at near-solidus conditions
and the corresponding pressure is known from Alin-hornblende barometry.
In order to estimate the maximum rate of magma
ascent in APT high-K calc-alkalic granitoids, those
having mEp with resorption textures armoured by
plagioclase phenocrysts have been selected. The
depth of emplacement of these granitoids, estimated
from Al-in-hornblende barometry, was about 5–7
kbar, which is similar to the minimum pressure for
occurrence of mEp enclosed in K-feldspar. Using the
apparent diffusion coefficient of elements ŽSi, Al, Ca
and Fe. between tonalitic melt and epidote at 7508C
Ž5 = 10y1 7 m2 sy1 . given by Brandon et al. Ž1996.,
dissolution inwards of 0.15–0.20 mm of epidote
crystal margins ŽFig. 9c and d. was completed in
40–180 years. Therefore, a transport rate from pressures around 10 to 6 kbar Ž; 12 km. of 70–350 m
yeary1 is required.
Survival of mEp in hornblende-free granitoids
emplaced in the Pampean Ranges, Argentina, can be
explained by rapid magma upward transport along
the Tafi Megafracture, active during Palaeozoic granitoid emplacement. For mEp-bearing granitoids in
the Famatina geological system, however the possibility of rapid upward transport of epidote is not
obvious.
Structural control of upward magma migration by
faults is obvious in most Chilean plutons under
consideration. Those plutons in the Elqui superunit
are elongated in the N–S direction and their emplacement was controlled by N–S trending faults,
and same can be said for the Santo Domingo and
Cuesta de Queulat plutons. The Mesozoic granodiorite at Puerto Chacabuco, although sharing similar
petrographicalrchemical characteristics with those in
the Elqui superunit, contains no epidote and it is
likely that this magma did not migrate upwards
rapidly enough to prevent a complete dissolution of
epidote.
7. Discussion
Several variables Žrock type, magma series, isotopic data, MS, host metamorphic grade, mol% Ps of
epidote, Al-in-hornblende barometry. have been
listed in Table 3 to permit assessment of common
features of mEp occurring in diverse plutons of
various tectonic settings, as described in this study.
Epidote is more abundant in plutons of the calcalkalic and high-K calc-alkalic magma series than in
the trondhjemitic and shoshonitic series. It is also
shown in this study that low MS is the rule and that
mEp is present in plutons of late collisional, inner
arc, compressional subduction and intra-arc slip fault
tectonic settings. These plutons intruded low, intermediate or high grade metamorphic rocks.
With few exceptions, the absence of iron oxides is
a major feature of these plutons. Schmidt and
Thompson Ž1996. observed that magnetite is the
main Feq3 -containing phase above epidote stability,
whereas at lower temperatures Feq3 tends to enter
epidote. In these plutons, it is probable true that
Feq3 and Ti have been accommodated by epidote
and titanite, respectively, obviating oxide saturation.
The fresh appearance of plagioclase in the plutons
in this study suggests that, in most cases, the rocks
have been subjected to minimal weathering and subsolidus alteration, supporting an igneous origin for
most epidotes observed in these plutons. In the
Guanta pluton, in Chile, plagioclase is sometimes
rather more altered and the amount of secondary
epidote is high, but textural relationships and the
compositions of some epidote grains suggest a magmatic origin.
Virtually all the textural features common to mEp
described by Zen and Hammarstrom Ž1984. are present in almost all the calc-alkalic and high-K calc-alkalic plutons of NE Brazil. In some of these plutons,
epidote encloses highly embayed hornblende, suggesting resorption of the hornblende and subsequent
precipitation of epidote in the magma. In other cases,
when the proportion of biotite to hornblende increases, the modal abundance of epidote also in-
(C ) Chile
High Andes Cordillera
Žpre-Andean .
Southern Coastal batholith
Žpre-Andean .
North Patagonian batholith
ŽAndean .
507"13 ŽRb – Sr.
422 ŽRb – Sr. Ž6 .
456"14 ŽRb – Sr.
Ž7 .
Ž6 .
600
627 ŽU – Pb . 618"9.5
ŽRb – Sr. Ž5 .
638"29 ŽRb – Sr. Ž4 .
633"0.9 ŽRb – Sr. Ž2 .
575 ŽU – Pb . Ž1 .
Age ŽMa .
Granodiorite to tonalite
Granodiorite to tonalite and granite
285"1.5 ŽU – Pb . Ž11 .
308"15 ŽRb – Sr. Ž13 .
14.6"0.4 ŽRb – Sr . Ž15 . Qz– diorite
Santo Domingo
Cuesta de Queulat
Tonalite to granodiorite
Tonalite
Tonalite to granodiorite
Porphyritic granodiorite to monzogranite
Porphyritic granodiorite
Porphyritic granodiorite to monzogranite
Porphyritic granodiorite
Leucocratic granodiorite to tonalite
Quartz monzonite to quartz syenite
Granodiorite to tonalite
Granodiorite to tonalite
Porphyritic qz monzonite to granite
Rock type
Guanta
Cerro Blanco
460 to 400 ŽRb – Sr. Ž8 .
Sierra de Paganzo
457; 404 ŽRb – Sr. Ž9 .
Sierra Chica de Cordoba 494"11 ŽRb – Sr. Ž10 .
Cafayate
Infiernillo
Famatina Geological System Cerro Toro
(B ) Argentina
Tafi Megafracture
Macurure´
Alto Pajeu´
Boa Ventura
Emas
Pedra Branca
Penaforte
St. Antonio
ˆ Creek
Brejinho
Tavares
Conceiçao
˜ das Crioulas
Caldeirao
˜ Encantado
Palmeira
Teixeira
Gloria Norte
Cel. Joao
˜ Sa´
Sao
˜ Rafael Batholith
(A ) NE Brazil
Serido´
Cachoeirinha– Salgueiro
Pluton
Terranergeological system
Table 3
Geological and geochemical features of representative epidote-bearing granitoid plutons in NE Brazil, Argentina and Chile
Sri
Calc-alkalic
Calc-alkalic
Calc-alkalic
0.7057 – 0.7098
Ž14 .
0.70367 Ž15 .
0.70627 Ž12 .
0.7043
0.7069
0.70607 to
0.70961 Ž8 .
0.70837 Ž5 .
y3.8 Ž6 .
Ž6 .
y7.0
y4.9 Ž15 .
y1.7 to y4.2 Ž14 .
y3.1 to y3.8 Ž12 .
y1.0 to
y3 to 0
y5.0 to
y4.2
y7.4 to y4.8 Ž5 .
y14.6 to y14.1
Trondhjemitic
Shoshonitic
Calc-alkalic
y2.0 to y1.0 Ž3 .
y3.6 to y3.5
0.70598
TDM ŽGa .
0.318 Ž15 .
0.9 – 1.5 Ž14 .
1.4
1.7
1.2 to 1.3 Ž6 .
1.46
1.3 to 1.7
2.15
1.32 to 1.42
1.20 to 1.40 Ž3 .
y23.0 to y18.0 Ž1 . 2.73 Ž1 .
´ Nd
High-K calc-alkalic 0.70933 Ž4 .
Calc-alkalic
High-K calc-alkalic 0.7130
Magma series
A.N. Sial et al.r Lithos 46 (1999) 367–392
387
q10.0 to q12.0
Alto Pajeu´
q10.0
For notes to Table 3 see next page.
Southern Coastal batholith
Žpre-Andean .
North Patagonian batholith
ŽAndean .
(C ) Chile
High Andes Cordillera
Žpre-Andean .
Famatina Geological System
(B ) Argentina
Tafi Megafracture
Macurure´
q11.0 to q13.0
Cachoeirinha– Salgueiro
q8.5 to q9.5
q10.0
q7.5 to q8.5
d 18 O sm ow Ž‰ .
(A ) NE Brazil
Serido´
Table 3 Žcontinued .
50.0
8.0 to 13.0
0.30
0.13
12.0
0.30
0.20
0.15
0.20
0.10
0.30 to 0.50
0.15 to 0.40
1.0 to 4.0
Magnetic
susceptibility
Ž=10 y3 SI.
Gneisses of the Chilenia
Terrane accreted to
Gondwana during Late
Devonian or Early
Carboniferous
Greenschist
to amphibolite facies
Low grade
metasedimentary rocks
Amphibolites facies
Žortoamphibolites,
micaschistis migmatites .
Ortoamphibolite
Amphibolite facies
Amphibolite facies
Žgarnet– biotite– gneisses,
amphibolite and marble .
Greenschist to
amphibolite facies
Amphibolite facies
High-grade gneisses,
quartizites, and schists
Amphibolite facies
Žmica schists and
limestones . and gneisses
Greenschist facies
Žmarine turbidites .;
kyanite-bearing thermal aureoles
Host metamorphic grade
5.0 to 6.0
4.0 to 4.5
650 to 660
660 to 680
645 to 655
660 to 680
680 to 690
5.0 Ž16 .
5.5 to 6.5 Ž16 .
4.5 to 5.5
670 to 680
6.5 to 7.5 Ž16 .
Hornblende-free
680 to 700
675 to 700
655 to 680
660 to 670
5.0 to 6.0
5.5 to 6.0
5.0 to 5.5
6.0 to 6.5
Hornblende-free
660 to 680
650 to 715
810
740
730
765
760
5.0 to 7.0
6.5 to 8.5
to
to
to
to
to
780
730
725
730
740
5.0
6.5
8
7.0
7.5
4.5
5.5
6.5
6.0
6.5
to
to
to
to
to
650 to 720
650 to 700
H and B
T Ž8C .
4.5 to 6.5
3.5 to 4.5 Ž16 .
Al-in-hbl
A and S
P Žkbar.
23 to 24
27 to 28
23 to 24
21 and 26 to 27
21 to 24
27 to 29
27 to 28
25 to 26
20 to 24
20 to 24
20 to 24
27 to 29
Ps epidote
Žmol% .
Intra-arc strike slip fault
ŽLiquine-Ofqui
Fault Zone .
˜
Compressional subduction
Compressional subduction
Inner Cordilleran
magmatic arc
collisional
Late collisional
Late collisional
Late collisional
Late collisional
Tectonic
ŽSetting .
388
A.N. Sial et al.r Lithos 46 (1999) 367–392
A.N. Sial et al.r Lithos 46 (1999) 367–392
creases. In such cases, the textural relationship of
epidote to biotite suggests that these two phases
crystallized simultaneously, according to the reaction: plagioclase q amphibole q liquid ™ biotite q
epidote. In the plutons of the Tafi Megafracture in
Argentina, these relationships are not so clear and
hornblende is virtually absent.
The overall compositional variation of epidote
Ž20–30 mol% Ps. is consistent with values proposed
by Johnston and Wyllie Ž1988, Fig. 5, p. 42., and by
Tulloch Ž1979. for mEp. There is a tendency, with
some exceptions, for 20–24 mol% Ps compositions
to occur in epidotes from plutons emplaced at, or
above, 5 kbar pressure, and compositions in the
27–29 mol% Ps range to occur in plutons emplaced
at lower pressures ŽTable 3..
Partially resorpted mEp crystals, in a large number of the studied plutons, suggest that this phase
sometimes exceeded its stability field after crystallization but survived complete dissolution by the
host melt due to relatively rapid upward melt transport. Alternatively, epidote armoured by biotite
andror by near-solidus K-feldspar in high-K calc-alkalic granitoids, also survived resorption by melt. In
this latter case, it is assumed that K-feldspar crystallized much more rapidly than the time scales for
epidote dissolution Ž- 10 2 years, according to Brandon et al., 1996..
Notes to Table 3:
A and S: Anderson and Smith Ž1995..
H and B: Holland and Blundy Ž1994..
Italicized age is from regional geologic consideration.
Ž1. Ketcham et al. Ž1995..
Ž2. Sial Ž1993..
Ž3. Van Schmus et al. Ž1995..
Ž4. Brasilino et al. Ž1997..
Ž5. Castellana Ž1994..
Ž6. Miller et al. Ž1991..
Ž7. Saavedra et al. Ž1996..
Ž8. Cisterna and Toselli Ž1991..
Ž9. Saal et al. Ž1996..
Ž10. Rapela et al. Ž1991..
Ž11. Pankhurst et al. Ž1996..
Ž12. Mpodozis and Kay Ž1992..
Ž13. Herve´ et al. Ž1988..
Ž14. Parada et al. Ž1998., this volume.
Ž15. Pankhurst et al. Ž1998..
Ž16. Rossi de Toselli et al. Ž1991..
389
8. Conclusions
Our current knowledge of mEp-bearing granitoids
in NE Brazil, Argentina and Chile leads us to the
following conclusions.
Ž1. Typically, Neoproterozoic mEp-bearing granitoids in NE Brazil have low MS, consistent with
experiments which indicate that iron oxide minerals
and mEp are mutually exclusive. Similar behavior is
observed in Early Palaeozoic plutons in Argentina
and Late Palaeozoic granitoids in Chile, with only a
few exceptions in which magnetite is present and
MS values higher than 10 = 10y3 SI are observed.
Ž2. mEp, recognized on textural grounds, can be
grouped into Ps 20 – 23 and Ps 27 – 29 compositional
ranges. Epidotes in the first group crystallized
buffered by the NNO or in the QFM to NNO range
at P f 5 kbar or above. In the second group, epidote
crystallized under P between 3 and 5 kbar and f O 2
between the NNO and HM range. Al-in-hornblende
barometry, in some cases, yields pressure estimates
corresponding to variation in composition of coexisting epidote.
Ž3. Preliminary estimates of upward migration
rates of high-K calc-alkalic magmas give values
ranging from - 100 m yeary1 up to 350 m yeary1 .
Ž4. The absence of epidote in granitoids Žhigh-K
calc-alkalic plutons adjacent to the northern bound-
390
A.N. Sial et al.r Lithos 46 (1999) 367–392
ary of the CST. that otherwise are identical to mEpbearing plutons described in this study Žhigh-K calcalkalic plutons in the APT. suggests that Ža. host
magma did not migrate upward sufficiently rapidly
to avoid complete dissolution of epidote or Žb. nearsolidus K-feldspar or biotite did not grow sufficiently rapidly to allow armouring of epidote before
its total dissolution, or Žc. that magma did not meet
the required compositional or f O 2 conditions to
crystallize epidote.
Acknowledgements
This project was partially supported by grants
from the Program of Support to the Scientific and
Technological Development ŽPADCTrFINEP, grant
no. 65.930.619-00. and from VITAE ŽB-11487r
3B001. to which we are thankful. We are also
grateful to Andrew Tulloch and to an anonymous
reviewer for comments and suggestions made on an
earlier version of this paper. This is the contribution
no. 118 of the Laboratory Nucleus for Granite Studies ŽNEG., Department of Geology, Federal University of Pernambuco, Brazil.
References
Anderson, J.L., 1996. Status of thermobarometry in granitic
batholiths. Trans. R. Soc. Edinburgh: Earth Sci. 87, 125–138.
Anderson, J.L., Smith, D.R., 1995. The effects of temperature and
fO 2 on the Al-in-hornblende barometer. Am. Mineral. 80,
549–559.
Baldis, B., Viramonte, J., Salfity, J., 1975. Geotectonica
de la
´
comarca compreendida entre el cratogeno
Central Argentino y
´
el borde Austral de la Puna. Actas, II Congreso Iberoamericano de Geologia Economica, Vol. 4. Buenos Aires, Argentina, pp. 45–44.
Belen Perez, M., Baldo, E.G., Saieg, A., Dominguez, J., 1996.
Tipologia de epidotos de granitoides de la Sierra Chica
Septentrional de Cordoba, Argentina, Universidad Nacional de
Jujuy. Revista Instituto de Geologia y Mineria 11 Ž1., 71–91.
Bohlen, S.R., Wall, V.J., Boettcher, A.L., 1983. Experimental
investigations and geological applications of equilibria in the
system FeO–TiO 2 –Al 2 O 3 –SiO 2 –H 2 O. Am. Mineral. 68,
1049–1058.
Brandon, A.D., Creaser, R.A., Chacko, T., 1996. Constraints on
rates of granitic magma transport from epidote dissolution
kinetics. Science 271, 1845–1848.
Brasilino, R.G., Sial, A.N., Ferreira, V.P., 1997. Subcrustal emplacement of the Conceiçao
˜ das Creoulas pluton of alto Pajeu´
terrane, NE Brazil: evidence from magmatic epidote and hornblende mineral chemistry. Second International Symp. on
Granites and Associated Mineralizations ŽISGAM., Extended
Abstracts, Salvador, Brazil, pp. 181–182.
Caby, R., Sial, A.N., 1996. Corneenes a disthene-staurotide-grenat
et profondeur de cristallisation de quelques plutons NE du
Bresil.
16 e Reunion Sci. de la Terre, Orleans,
Soc. Geol.,
´
´
´
France, p. 87.
Castellana, D.H., 1994. Age and origin of the Coronel Joao
˜ Sa´
pluton, Bahia, Brazil. MS thesis, Univ. of Texas, Austin, 137
p.
Cisterna, C., Toselli, A.J., 1991. San Agustin sus rocas basicas.
´
In: Acenolaza,
F.G., Miller, H., Toselli, A.J. ŽEds.., Geologıa
˜
´
del Sistema de Famatrina. Munchener
Geologsche Hefte ŽRe¨
ihe A., Munich, pp. 187–198.
Davison, I., Santos, R., 1989. Tectonic evolution of the Sergipano
Fold Belt, NE Brazil, during the Brasiliano Orogeny. Precamb.
Res. 45, 319–342.
Dawes, R.L., Evans, B.W., 1991. Mineralogy and geothermometry of magmatic epidote-bearing dikes, Front Range, Colorado.
Geol. Soc. Bull. 103, 1017–1031.
Evans, B.W., Vance, J.A., 1987. Epidote phenocrysts in dacitic
dikes, Boulder county, Colorado. Contrib. Mineral. Petrol. 96,
178–185.
Farrow, C.E.G., Barr, S.M., 1992. Petrology of high-Al-hornblende and magmatic epidote-bearing plutons in the southeastern Cape Breton Highlands, Nova Scotia. Can. Mineral. 30,
377–392.
Ferreira, V.P., Sial, A.N., Santos, E.J. Jardim de Sa,
´ E.F.,
Medeiros, V.C., 1997. Granitoids in the characterization of
terranes: the Borborema Province, northeastern Brazil. Second
International Symp. On Granites and Assoc. Mineral.
ŽISGAM., Salvador, Brazil, pp. 197–201.
Galindo, A.C., 1993. Petrologia dos granitoides Brasilianos da
regiao
e Umarizal ŽOeste do Rio Grande do
˜ de Caraubas
´
Norte.. Doctoral Thesis, Federal Univ. of Para,
´ Belem,
´ Brazil,
386 p.
Ghent, E.D., Nicholls, J., Simony, P.S., Sevigny, J.H., Stout,
M.Z., 1991. Hornblende geobarometry of the Nelson Batholith,
southeastern British Columbia: tectonic implications. Can. J.
Earth Sci. 2, 1982–1991.
Hammarstrom, J.M., Zen, E., 1986. Aluminum in hornblende: an
empirical igneous geobarometer. Am. Mineral 71, 1297–1313.
Herve,
´ F., Munizaga, F., Parada, M.A., Brook, M., Pankhurst,
R.J., Snelling, N.J., Drake, R., 1988. Granitoides of the Coast
Range of central Chile: geochronology and geologic setting. J.
South Am. Earth Sci. 1, 185–194.
Holland, T., Blundy, J., 1994. Non-ideal interactions in calcic
amphiboles and their bearing on amphibole–plagioclase thermometry. Contrib. Mineral. Petrol. 116, 433–447.
Hollister, L.S., Grissom, G.C., Peters, E.K., Stowell, H.H., Sissom, V.B., 1987. Confirmation of the empirical correlation of
A.N. Sial et al.r Lithos 46 (1999) 367–392
Al in hornblende with pressure of solidification of calc-alkaline plutons. Am. Mineral. 72, 231–239.
Ishihara, S., 1977. The magnetite-series and ilmenite-series granitic
rocks. Mining Geology 27, 293–305.
Johnson, M.C., Rutherford, M.J., 1989. Experimental calibration
of the aluminum-in-hornblende geobarometer with application
to Long Valley caldera ŽCalifornia. volcanic rocks. Geology
17, 837–841.
Johnston, A.D., Wyllie, P.J., 1988. Constraints on the origin of
Archean trondhjejemites based on phase relationships of Nuk
gneiss with H 2 O at 15 kbar. Contrib. Mineral. Petrol. 100,
35–46.
Ketcham, D., Long, L.E., Sial, A.N., 1995. Rb–Sr and Sm–Nd
study of the Sao
˜ Rafael batholith, Rio Grande do Norte,
Northeast Brazil. 3rd Hutton Symp., U.S. Geol. Survey circ.
1129. College Park, MD, pp. 79–80.
Keyes, C.R., 1893. Epidote as a primary component of eruptive
rocks. Geol. Soc. Am. Bull. 4, 305–312.
das rochas
Lima, E.S., 1987. Evoluçao
˜ termobarometrica
´
metapelıticas
da regiao
´
˜ do Serido.
´ Rev. Bras. Geoc. 17 Ž3.,
315–323.
Liou, J.G., 1973. Synthesis and stability relations of epidote,
Ca 2 Al 2 FeSiO 3 O12 ŽOH.. J. Petrol. 14, 381–413.
McReath, I., Lafon, J.M., Chaves, J.M., Conceiçao,
˜ H., 1993.
Strontium and evidence for complex petrogenesis in the Coronel Joao
˜ Sa´ intrusion, Sergipe Fold Belt. 40th Brazilian Geochemical Congress, Brasilia, Brazil, pp. 86–89.
McReath, I., Lafon, J.M., Davison, I., Chaves, J.M., Conceiçao,
˜ in
press. Late tectonic Brasiliano-age granitoids in the Sergipano
Fold belt ŽNE Brazil.: the Coronel Joao
˜ Sa´ pluton and its
tectonic and petrogenetic implications. J. South Am. Earth Sci.
Miller, C.F., Pankhurst, R.J., Rapela, C.W., Saavedra, J., Toselli,
A., 1991. Genesis de los granitoides Paleozoicos peraluminosos, areas Tafi del Valle y Cafayate Sierras Pampeanas,
Argentina. 6 Congreso Geologico
Chileno, Vina
´
˜ del Mar,
Chile, Extended Abstracts, pp. 36–39.
Mpodozis, C., Kay, S., 1992. Late Paleozoic to Triassic evolution
of the Gondwana margin: evidence from Chilean Frontal
Cordillera batholiths Ž288S to 318S.. Geol. Soc. Am. Bull. 104,
999–1014.
Naney, M.T., 1983. Phase equilibria of rock-forming ferromagnesian silicates in granitic systems. Am. J. Sci. 283, 993–1033.
Owen, J.V., 1991. Significance of epidote in orbicular diorite
from the Grenville Front Zone, eastern Labrador. Mineral.
Mag. 55, 173–181.
Pankhurst, R.J., Millar, I.L., Herve,
´ F., 1996. A permo-carboniferous U–Pb age for part of the Guanta unit of the Elqui–Limari
Batholith at Rio de Transito,
Northern Chile. Revista Geologica
´
´
de Chile 23, 35–42.
Pankhurst, R.J., Weaver, S.D., Herve,
´ F., Larrondo, P., 1998.
Geochronology and geochemistry of the North Patagonian
batholith in Aysen,
´ southern Chile. J. Geol. Soc. London,
submitted.
Parada, M.A., 1990. Granitoid plutonism in central Chile and its
geodynamic implications: a review. Geol. Soc. Am. 241,
51–66, Special paper.
Parada, M.A., Nystrom, J., Levi, B., 1998. Multiple sources for
391
the coastal batholith of Central Chile Ž318–348S.: geochemical
and Sr–Nd isotopic evidence. Lithos, this volume.
Piwinskii, A.J., Wyllie, P.J., 1968. Experimental studies of igneous rocks series: a zoned pluton in the Wallowa Batholith.
Oregon J. Geol. 76, 205–234.
Rapela, C.W., 1976. Las rocas granitoides de la region de Cafayate, Provıncia
de Salta: aspectos petrologicos
y geoquımicos.
´
´
´
Revista Asociacion
Argentina 31, 260–278.
´ Geologica
´
Rapela, C.W., Shaw, D.M., 1979. Trace and major element
models of granitoid genesis in the Pampean Ranges, Argentina. Geochim. Cosmochim. Acta 43, 1117–1129.
Rapela, C.W., Heaman, L.M., McNutt, R.H., 1982. Geochronology of granitoid rocks from the Pampean Ranges, Argentina.
J. Geol. 90 Ž5., 574–582.
Rapela, C.W., Pankhurst, R.J., Bonaluni, A.A., 1991. Edad y
geoquımica
del porfido
granıticos
de Oncan,
´
´
´
´ Sierra Norte de
Cordoba,
Sierras Pampeanas, Argentina. 6 Congr. Geol.
´
Chileno, Vina del Mar, Vol. 1, pp. 19–22.
Rogers, J., 1988. The arsiukere granite of Southern India: magmatism and metamorphism in a previously depleted crust. Chem.
Geol. 67, 155–163.
Rossi de Toselli, J.N., Toselli, A.J., Wagner, S.J., 1991. Geobarometria de hornblendas en granitoides calcoalcalinos: Sistema de Famatina, Argentina. 6 Congreso Geologico Chileno,
Vina
˜ del Mar, Chile, Extended Abstracts, pp. 244–247.
Saal, A., Toselli, A.J., Rossi de Toselli, J.N., 1996. Granitoides y
rocas basicas
de al Sierra Paganzo. In: Acenolaza,
F.G.,
´
˜
Miller, H., Toselli, A.J. ŽEds.., Geologıa
´ del Sistema de
Famatina. Munchener
Geologische Hefte ŽReihe A., Munich,
¨
pp. 229–240.
Saavedra, J., Toselli, A.J., Rossi de Toselli, J.N., 1996. Granitoides y rocas basicas
de la Sierra de Paganzo. In: Acenolaza,
´
˜
F.G., Miller, H., Toselli ŽEds.., Geologia del Sistema de
Famatina. Munchener Geologische Hefte 19 ŽReihe A., pp.
229–240.
Schmidt, M.W., 1992. Amphibole composition in tonalite as a
function of pressure: an experimental calibration of the Al-inhornblende barometer. Contrib. Mineral. Petrol. 110, 304–310.
Schmidt, M.W., Thompson, A.B., 1996. Epidote in calc-alkaline
magmas: an experimental study of stability, phase relationships, and the role of epidote in magmatic evolution. Am.
Mineral. 81, 424–474.
Sial, A.N., 1986. Granite-types in Northeastern Brazil, current
knowledge. Rev. Bras. Geoc. 16 Ž1., 54–72.
Sial, A.N., 1990. Epidote-bearing calc-alkalic granitoids in Northeast Brazil. Rev. Bras. Geoc. 20 Ž1–4., 88–100.
Sial, A.N., 1993. Contrasting metaluminous magmatic epidotebearing granitic suites from two precambrian foldbelts in
Northeast Brazil. An. Acad. Bras. Ci. 65, 141–162, suppl. 1.
Sial, A.N., Ferreira, V.P., 1988. Brasiliano age peralkaline plutonic rocks of the central structural domain, Northeast Brazil.
Rendiconti della Soc. Italiana di Miner. e Petrol. 43 Ž2.,
307–342.
Sial, A.N., Toselli, A.J., Saavedra, J., Ferreira, V.P., Rossi de
Toselli, J.N., 1995. Magmatic epidote-bearing granitoids from
NW Argentina and NE Brazil. 3rd Hutton Symp., U.S. Geol.
Survey circ. 1129. College Park, MD, pp. 141-142.
392
A.N. Sial et al.r Lithos 46 (1999) 367–392
Takahashi, M., Aramaki, S., Ishihara, S., 1980. Magnetiteseriesrilmenite-series vs. I-typerS-type granitoids. Mining
Geology Special Issue 8, 13–28.
Thomas, W.M., Ernst, W.G., 1990. The aluminium content of
hornblende in calc-alkaline granitic rocks: a mineralogic
barometer calibrated experimentally to 12 kbar, Vol. 2. In:
Spencer, R.J., Shou, I.-M. ŽEds.., Fluid Mineral Interactions:
A Tribute to H.P. Eugster. Geochem. Soc., special publication,
pp. 59–63.
Toselli, A.J., Saavedra, J., Lopez, J.P., 1997. Magmatic epidotebearing and cordierite-bearing granitoids from NW Argentina.
Second International Symp. on Granites and Associated Mineralizations ŽISGAM.. Excursions Guide, Salvador, Brazil, pp.
79–106.
Tulloch, A., 1979. Secondary Ca–Al silicates as low-grade alteration products of granitoid biotite. Contrib. Mineral. Petrol.
69, 105–117.
Van Schmus, W.R., Brito Neves, B.B., Hackspacker, P., Babinski,
M., 1995. UrPb and SmrNd geochronologic studies of the
eastern Borborema Province, Northeastern Brazil: initial conclusions. J. South Am. Earth Sci. 8, 267–288.
Vyhnal, C.R., McSween, H.Y. Jr., Speer, J.A., 1991. Hornblende
chemistry in southern Appalachian granitoids: implications for
aluminum hornblende thermobarometry and magmatic epidote
stability. Am. Mineral. 76, 176–188.
Watson, E.B., 1987. The role of accessory minerals in granitoid
geochemistry. Hutton Conference on the Origin of Granites,
Univ. of Edinburgh, pp. 209–211.
Watson, E.B., Harrison, T.M., 1983. Zircon saturation revisited:
temperature and compositional effects in a variety of crustal
magma types. Earth Planet. Sci. Lett. 64, 295–304.
Xu, G., Wil, T.M., Powell, R., 1994. A calculated petrogenetic
grid for the system K 2 O–FeO–MgO–Al 2 O 3 –SiO 2 –H 2 O,
with particular references to contact-metamorphosed pelites. J.
Met. Geol. 12 Ž1., 99–119.
Zen, E., Hammarstrom, J.M., 1984. Magmatic epidote and its
petrologic significance. Geology 12, 515–518.